The game is played with a single deck of cards.
Dealer hits a soft 17.
Player may double after a split.
Player may resplit to up to four hands, including aces.
Player may hit and double down to split aces.
Player may double on any number of cards.
Player may take late surrender on any number of cards.
Player may surrender half of total bet after doubling.
A player hand totaling 20 or less, consisting of six cards or more, except after doubling, automatically wins.
A player hand of 21 points, consisting of 5 cards or more, except after doubling, pays 2 to 1 instantly.
A player blackjack always wins
A player blackjack in diamonds pays 2 to 1, all other blackjacks pay even money.

Double Down Rescue Strategy: The player should surrender after doubling down if his total is 12-16 and the dealer is showing an 8-ace.

Some readers may question why the player should normally surrender on a 3-card 17 against an ace but not if after a double down. The reason is composition dependent. The player will only double down in the first place if the first two cards total 10 or 11. After the third card the player has already removed at least one 7, 8, or 9 from the deck, decreasing the dealer's probability of making a 18-20. The 3-card compositions that favor surrendering are A+6+10, 2+5+10, and 3+4+10. None of these are possible following the basic strategy after a double.

House Edge
According to my own combinatorial analysis the house edge is 0.94%.
I have a report that at the MGM Grand the dealer stands on a soft 17. This should lower the house edge to 0.75%.